We live in an area where there's a relatively high water table, so our sump pump runs on a regular basis. Typically not a huge quantity of water (unless there's been a bunch of recent rains), but the pump will occasionally run for about 9 months of the year. Since our basement is mostly finished, I thought it to be critical to not only have a battery backup, but also a second functioning pump in case the primary one failed. My sump pit was plenty big, so my pit has two pumps in parallel. One is the standard 110v pump with float switch, and the second is a completely independent 12V pump with its own float switch. The 12V backup pump is run from a deep cycle marine battery with its own trickle charger and it all came as a set, except for the battery. I think the brand is Zoeller, but can't recall for sure.
The backup doesn't have nearly the pumping capacity of the main pump, but it will still drain the sump plenty fast for our needs. Just need to make sure the battery is replaced every few years even if it hasn't been used.
One thing I needed to do was put check valves after each pump (and before the two pump lines joined to go out of the house), or else one would just pump into the other and not remove much of any water. Don't skimp on the quality of the check valve, as I had one fail shortly after installation, and so I was just pumping out of my main pump and backwards through my backup pump.
Also, one other thing I have done is to have a spare 110V sump pump already purchased, along with all needed PVC pipe, attachments, and Fernco couplings to make quick work of changing out my main sump pump when (and not if) it eventually fails. History has proven (thankfully not directly to me) that sump pumps will often fail at the worst times (middle of the night, or after very heavy rains and the stores are sold out of replacement pumps), and it's nice to know that I have a replacement pump ready to go, just in case.
Finally, home insurance policies often don't cover sump pump failures, so check your insurance policy. In our case, it was quite inexpensive to add a separate sewer/water backup rider to our policy which covers sewage backups, water backups, etc.
The importance of having a good sump pump system and backups should be inversely proportional to the amount of damage you're willing to accept and pay for if something fails in your current pump system. If you don't care about potential damage, the importance is low. If you have valuable things in your basement that could be damaged, then the importance of having backups and insurance coverage is high.