Does EurailPass holder must make train reservation for Florence to Milan and Venice to Florence?
Have you already bought your Eurail Pass? They tend to cost more than point-to-point tickets in Italy.
You mean buy a point-to-point train ticket locally is cheaper than Eurailpass?
Sure, all Italian rails, except Regionals, require a seat reservation that varies pricewise depending on the train. Regional trains do not have reservations so you can jump on any Regional train. With advance purchase discounts, the surcharges for reservations, etc. it generally cheaper for p2p. BUT, the only way to know for sure is to do your homework and price your route then compare that to the pass price.
In Italy, point to point tickets are cheaper than railpasses. Maybe in other European countries they are a good buy, but not in Italy (generally). I stay 14-17 days in Italy on my yearly trips....3-4 days in each town....meaning I don't travel by train everyday......and I always buy my tickets when I am in country...not online before. Never had a problem.
Point-to-point tickets in Italy are much cheaper than EurailPass, but if you already have the pass, you will need to make reservations. I think there is a fee for this. If you don't already have the pass, buy point-to-point tickets - none of the cities you mention is really far enough apart to make the pass cost-effective.
Swiss Rail Passes are a good value in Switzerland, but Eurail Passes have less advantage. I just don't think it's a good idea any more to purchase Eurail Passes and then have to pay additional for reservations and such.
LoLa, if you travel by regional train, be sure to validate your ticket at the little box at the railhead before you jump on the train. Intercity and faster trains have reserved seating.