Using the LCM method gives the more accurate value while dividing the individual value will also gives the same value but not always.
Two 2Ω resistors in parallel
1R=12+12
Method 1
Taking LCM
R=2×22+2
=1Ω
Method 2
Individually dividing the values we get
R=0.5+0.5
=1Ω
Three 3Ω resistors in parallel
1R=13+13+13
Method 1
Taking LCM
R=33
=1Ω
Method 2
Individually dividing the values we get
R=0.33+0.33+0.33
=0.99Ω