To me the biggest pain in pH measurement is calibrating the meter. Once that is done it's good for the rest of the day and measurements themselves are easy to make once you have a cooling scheme that works figured out (I use a small metal saucepan - dip it into the mash tun or kettle and then float in a couple of inches of cold water in the brewery sink).
Experience with pH readings taken at various points throughout the brewing process can serve as checkpoints for subsequent brews. Thus, IMO, you should take lots. At dough in, 10 and 20 minutes into the first rest, at the completion of each rest, coming out of lauter and and the end of the boil. Then in the fermenter every few hours and then every day or 2 and then finally in the finished beer.
There is plenty of discussion about what the initial mash pH should be. The readings beyond that lend assurance that the process is going normally. If you are used to seeing pH drop 0.15 in the kettle and it only drops 0.05 then you know something is wrong (or at least different) and should try to figure out why.
One of the most comforting applications is in checking that the fermentation is starting normally. Yeast will drop the pH of properly fermenting beer hours before any visible signs are apparent. This is especially the case if enclosed (such as cylindroconical) fermentors are being used. A drop of 0.2 pH or more in the first few hours is a pretty sure sign that a healthy fermentation is underway.