A bonsai needs to be clipped or pruned or trimmed mainly to increase ramification to obtain an old tree like appearance and to induce new growth. Clipping is absolutely necessary during active growth of all varieties of bonsai.
There are two ways of clipping/pruning bonsai:
a) hard pruning, medium to light
clipping and
b) pinching growing tips.
Concave cutters (a specialized bonsai tool) for heavy parts of the bonsai and medium / light duty scissors are used for clipping/pruning medium to thin branches; for pinching the tips of small branchlets or the growing ends usually the tips of the forefinger and the thumb are used. While pruning with concave cutters the cut can be made flush to the point of removal which helps to heal the wound. When pruning with scissors, the cut is made slightly above a leaf so as not to disturb the axial bud present at the junction of branch and leaf. Changes in the direction or movement of the branch is achieved by cutting just above any leaf which is pointing towards the direction in which a shoot is required. As a mature, well branched and ramified look is desired in a bonsai, the general downward inclination of the branches can sometimes be achieved simply be clipping growth just above a downward or side wards facing leaf in every branch, secondary and tertiary branches.
Clipping, which generally the cutting of smaller branches is also useful in thinning out overcrowded areas of growth and inward growing branchlets. Usually encouraging outward growing secondary/ tertiary branches can be encouraged by clipping alone and by clipping off or shortening inward growing shoots.
Pinching on the other hand is clipping off new growth/shoots by holding new unwanted growing tips with the firefinger and thumb and removing them with a twisting action or by using the nails to pinch off the tips. Thus clipping in any form is extremely useful in achieving ramified growth.