"Limit" calculates the bilateral limit but SymPy does just limit from the left or right. So for bilateral limit, limit from both directions are calculated and compared, if equal the bilateral limit exists or else does not exist. So this explain the bilateral limit calculation takes more time (i.e., double) than from the left or right.

SymPy sintax for limit of 1/x when x approaches 0 from the right (default direction) :
>>> limit(1/x,x,0)
>>> limit(1/x,x,0,dir='+')
which is infinity. From the left :
>>> limit(1/x,x,0,dir='-')
yields - infinity.

Using SymPy directly is useful when a sequence of calculations is needed. Because "Limit" is restricted to just calculate limits with many simplify, output, etc, options.