My partner and I have recently bought a house.
I'm going to get new door lock cylinders for the front and back door. I'm not sure whether to get them keyed alike.
Is it a bad idea to get them so that they use the same key?
If you lose the keys, or need to give them to someone who you later come to distrust, or post a picture of them on the internet then you'll need to change both locks instead of just one.
If this is just two doors, then it's not really a big deal - slightly more inconvenient if things go wrong weighed against slightly more convenience in everyday life.
(Note that a 'lost keys' insurance policy may not pay out to have both locks changed if you lose the keys - it's a conversation you'd need to have with the insurer prior to purchasing the policy.)
Since you're dealing with a real locksmith, it's a simple matter to have 2 tiers of key.
You have the "master key" which works every lock in the house.
Then you have the "contractor key" which only works certain doorknobs (but not the deadbolt there).
Mechanically, this is done one of two ways: Either fitting a double pin for one of the 5-7 pins, or simply removing that pin altogether.
The doorknob locks get a key that accepts either depth 2 or depth 7 on pin 6; or that doesn't check pin 6 at all. (the deadbolt locks require depth 7). You give the contractor a key with a cut of depth 2. Works in the doorknob, not the deadbolt.
The words "Do Not Duplicate" stamped on a key mean nothing. The key-duplicating robot at Lowes is illiterate. (I mean the actual robot, no judgment on any human clerk). However, un-duplicate-able keys are a thing.
Since you're going to a real locksmith, you can "nip the key-duplication issue in the bud", by using a non-duplicatable key system like Primus or Medeco. These keys have a second cut that can only practically be made at the factory.
The primary cut can be applied by any locksmith in the normal way. But the controlled second-cut is assigned to the locksmith. Your secondary cut will be shared with your locksmith's other customers of that system. I like using locksmiths 50 miles away, for that reason :) But no one could duplicate your key unless they stole a key from one of your locksmith's other customers, and then modified it with brazing to add material to re-cut it to your pattern. Not gonna happen.
I recently did a Medeco system and it was priced at $120 per core, though we opted for "figure 8" field-replaceable cores. Our Class II (but good Class II) hardware was $200 per knobset and $80 per deadbolt set and $60 per padlock, but you can get any figure-8 hardware; the magic is in the cores.
If they are just standard doorknob entry sets, I see no reason to key them differently. If you add deadbolts, then those should have different keys. I have often encouraged people to install a deadbolt without a key for additional inside protection but maybe not a good idea if you have small children or a spouse/partner who gets mad easily.
How handy are you? On this forum, I assume that you know which end of the screw driver to grab.
The big difference is the hassle of re-keying multiple locks if you want to deny a keyholder access.
Getting a lock rekeyed is straight forward. You don't even have to have the lock smith come to your house. Remove the locks, take them in, and a decent smith can do it in a few mintutes each. At one point our local hardware store could do it, and charged about twice what cutting a key cost. You only need to change one pin, and if you change it to a longer pin (shorter tooth on the key) you can regrind your existing keys.
If you live alone, make two trips, one with the latchsets and one with the deadbolts.
We got all of ours keyed alike and really enjoy the convenience of it, never had any issues even living in a so so neighborhood. We did recently change our gate locks to electronic keyless with solar battery backup due to the locks wearing out and not being able to get the same locks again without rekeying the new ones.