Like others have said, you risk being deleted if you don't visit your friends, plus it still counts as FP points so you can either collect those or get an occasional free donut. By visiting friends they at least get an extra 15 emblems because you did what any good friend would do "visit your friends"
I've deleted 10 friends from my list today as they haven't visited once during the new event, why because they collected their 60 emblems from people starting at #1-a in their list, I fall at "r" so get missed a lot by selfish or lazy friends. Mind you I started out with about 5 friends visiting a day, now I get an average of 20 per day, not bad when you consider I've got 70 friends in my list.
I'm not a greedy player and don't visit friends and only hit their lodge for the 5 emblems or just get my 60, I visit each friend everyday regardless of an event or not. I might need points etc but so do my friends, especially the new players.
Friends in my list don't get deleted if they are rebuilding, if they haven't visited their town for 3 weeks I just think they are on holidays and wait until the fourth week to see what happens, friends don't need to visit me daily but if they ignore me continuously bye bye