We are at about 350 dives, a good portion of those are shore reef dives alone w my buddy (husband). I read once, "every time you communicate with your buddy, ask them their air consumption & vice versa". And when checking the spg, also check depth, time of dive, NLD, & oxygen/nitrox loading. It seemed reasonable, So, I do.
Before beginning our dive, we have agreed on a dive plan - a turn around time/depth, max depth, & general direction based on current - all which provide a basic idea of what our air should be at certain points in our dive (based on time, current, & depth). Therefore, when checking, I usually have a "guess-timate" air amount in mind & I check to confirm I am around where I think we should be at that point in the dive. Sometimes, if we are communicating a lot, (back & forth) we won't keep asking each other, but I am risk adverse, somewhat Obsessive, so I tend to check frequently. Also, my husband burns his air more quickly than I, so I do want to keep track of his air, anyway, & not just mine.
As the OP questioned, I have also considered the possibility of becoming complacent after diving for awhile, & have decided to I'd rather be OCD about our air, than wish I had.