By establishing a block library, you and your co-workers won't have to worry about conflicting drafting practices. Even with a simple electrical out let, one person may make the circle bigger or smaller, the projection lines may be longer, shorter or spaced apart differently. Taking these factors into consideration, a final plotted drawing with non-uniform looking symbols can cause confusion for the client, and embarrassment for the company who designed the job. One of the best reasons for using blocks is the ease of changing its properties globally. Let's say you wish to change the radius of the circle because it's just a tad too big, you can glob ally change the properties of the symbol simply by redefining the block after you've made the necessary changes to an exploded version.
Blocks also help maintain layer, colour and linetype consistency.
Blocks that contain attributes are yet another great time saver. One good example of a block with attributes is your company title-sheet. Having inconsistencies with drafting symbols is bad enough, but having inconsistencies in the company title-sheet will be totally unacceptable. If you must copy or move a symbol, you only have t o select one entity. Attribute text will always maintain the same height, style, justification, position and pen thickness.