Seat reservation

My girlfriend and I have just finished booking pretty much everything for our upcoming eurotrip this august !!!! We have booked our hotels and hostels and 2 inter-europe flights for longer trips. We have also bought an Eurail pass for the other trips. We bought the 3 country 6 days pass (even if we will be having 7 train trips, one will be very cheap).

My question is : should we reserve seats for train trips that only go daily (like the Barcelona to Nice or the Nice to Genova). Should we reserve them today or wait to reserve them when we arrive in the cities from which we leave ?