Where to start... this is like asking how dimensions are helpful.
Any information that you want to use to control or document your model should be created as a parameter. For example, you can create parameters for things like part number, designer, supplier, cage code, etc. Or maybe you have some factor that you want to use in relations. For example, a minimum distance to part edge / hole diameter ratio. Create a parameter called edge_dist_dia_ratio, then write a relation like d2 = d1 * edge_dist_dia_ratio, where d2 is the distance dimension and d1 is hole diameter. The uses are endless.
Dave's correct, where to start. I do alot of sheetmetal, so my list would/might be shorter that others. MTL material; ISR inside bend radius; OSR outside bend radius (which is then a relation - OSR=MTL+ISR). Instead of just having a hole that is d2=4.500, why not create a parameter called HOLE1 and make that = to 4.500. Then all the time you need a 4.500 hole, just type in HOLE1 in the value.
parameters would be helpful in several ways as they toldu u can also use parameters to parametrise yoru job consider u are making a block u can define l b h as parameters and u can make the required size at any time when u require
I use parameters to define default part thickness (THICKNESS), default radii (NOM_RADII) and nominal draft (NOM_DRAFT). When creating the notes on the drawing, I use &thickness etc. to put in the notes. All part dimensions relating to parameters are controlled by a relationship, eg. &d25=thickness. In order to change the complete part thickness, all a user has to do is change the parameter shown on the print. There are many uses for parameters, above is just an example.