Trying to get back to your original question, while it is important to
remember that there are considerable differences between different gliders
(and generations of glider) some of the practical differences that you
might encounter include:

(1) Increased workload on the ground run (some flapped gliders need a
change from negative to positive flaps to prevent a wing dropping)

(2) Easier unstick once in a positive flap setting. Only really a factor
if launching from a short airfield or behind a low power tug.

(3) Lower thermaling speeds, particularly when heavy (so generally better
climb rates)

(4) Reduced roll control in positive flap settings, particularly in older
designs. This can be a factor when manoeuvring in a busy thermal and/or
lower down. In my experience not a major factor in more modern types

(4) Higher workload in flight (you need to consider what flap setting you
need)

(5) Steeper approach attitude, so better visibility and potential to land
shorter (very type specific)

(6) Increased workload on the landing run (some, particular older, flapped
gliders need a move to negative flap on the ground run to maintain roll
control

Some are positive, some negative, but if used properly, you will definitely
get a performance benefit on most cross country days, provided you get the
flap settings right. The price of the performance increase is a higher
workload. In my view, whether this trade off is worthwhile is sometimes as
much about you and your capacity/experience as the other factors.