I prefer one but if you are shooting mild or mid-level loads, I think you'll be safe not using one. If you're going to be loading near book max, I think they are advisable.
Most of my experience is with rifles but the same principles apply. For one thing traditional pressure signs like flat primers and sticky extraction only happen when you are WAY overloaded. Loads that are slightly over pressure will look and shoot just fine.
I was working on a load for a 300 WSM and 180 gr bullets a few years ago. Using a max load of H4350 I was getting 2950 fps, which was exactly what the load manuals showed for that load. All was good and accuracy was good.
But I'd read that RE17 would give me another 100 fps so I decided to try it. I loaded up some loads several gr below max and 3 loads each in .5 gr increments up to book max.
At the range, using my chronograph, I was still about 1.5 gr below book max, but my velocity was exceeding what I should have been getting with another 1.5 gr of powder, and accuracy wasn't what I'd hoped for. I stopped at that point and never fired the other loads.
To get the accuracy I wanted I wasn't getting any more speed than using H4350. Which is the powder I stayed with.
All barrels are different. RE17 didn't work with my rifle but lots of others have used it with good results. That is the ONLY time I've had that happen to me. Every other cartridge and powder combo I've used gave me predictable velocities. I would have been fine not using a chronograph for all other situations. But that one time it paid off.