I have 168 in begging and have yet to see any results. I just hit it once before auto attack just to keep it high. If there is a use for it someone can tell us.
The skill of conjuration works with some or your spells. Some are evocation, some are alteration, etc. These skills are absolutely critical to keep up. You can use your lowest level spells, for each type of skill. Right click on a spell, in your spellbook, and it will tell you the level, the type of skill, etc., so to practice use a low level, low mana skill. Magic skills more or less max at your level times 5, plus 5. Keep them as high as you can.
You do need to purchase spells one time, per spell. You cannot put them into your spell book, unless you are at the level shown on the scroll.