I'm sure that if you searched the internet for instructions <brand> <model> for the old water filter system, you'd find that it has, for whatever reason, a drain line. This drain line was tapped into the PVC tail pipe so it wouldn't flood your sink cabinet.

If your new water filter system also has a drain line, then you've already got a handy place to attach it, so no, you shouldn't replace this tail piece. If the new drain line is much smaller than the existing hole, you'll probably need to replace it anyway.

If your new filter system does not have a drain line, then it's pretty much guaranteed that if you run water down this drain now, you'll get water under your cabinet, so it is highly recommended that you replace this piece of pipe with a hole in it with a new one without a hole in it.

I'm sure that if you searched the internet for instructions <brand> <model> for the old water filter system, you'd find that it has, for whatever reason, a drain line. This drain line was tapped into the PVC tail pipe so it wouldn't flood your sink cabinet.

If your new water filter system also has a drain line, then you've already got a handy place to attach it, so no, you shouldn't replace this tail piece. If the new drain line is much smaller than the existing hole, you'll probably need to replace it and make a hole suitable for the drain of the new filter.

If your new filter system does not have a drain line, then it's pretty much guaranteed that if you run water down this drain now, you'll get water under your cabinet, so it is highly recommended that you replace this piece of pipe with a hole in it with a new one without a hole in it.