depends on the applications...considering weigh, space and cost.
and the different in resistence... how much thicker do you need to
make the difference.
resistence will be considered if you need to carry very high
current.
example 1:
your souce is 10V and your wire have a resistence of 0.1 ohms.
If you design it to carry 1 Amp your voltage drop will only be
0.1V
by doubling the cross-sectional area you cut down
resistence to 0.06 ohms. Your voltage drop will be 0.06V.
the difference will only be 0.04V... is this 0.04V different
important?
your end load will still receive 9.96V.
example 2:
now your 0.1 Ohms wire need to carry 50 Amp.
voltage drop will be 5V across wire, your end load receive only
5 V then...
by doubling cross-sectional area, resistence drop to 0.06 ohms.
your voltage drop across wire will only be 3 V
so by changing wire size you recover 2V, which does make some
different...