It refers to the amount of "prongs" on the aerial. The more elements you have the better the gain, so more signal is received. Generally, the further you are from the transmitter the more elements you need.
Again, as Timo says, the more elements the more gain, an aerial installer will generally know his local area and pick an aerial to suit local reception conditions. You also have to take into account 4G signals in the area, which if strong, may necessitate using an aerial which rejects most of the 800mhz range and or a masthead LTE filter. I use the Vision 36 element superlog for many of my installations, it has a tuning stub which eradicates a proportion of the 4G signal. http://www.vision-products.co.uk/catalogue/product/V10-36L . For parts of the area with strong signal I use a mini log, they're very compact with limited gain, but in a good signal area can still provide enough signal to drive a multipoint passive system and offer very little wind resistance, so a light chimney rig can be used. http://www.triax.com/FindProduct/ProductDetails.aspx?product={EF3FC918-7F6D-4F2D-AEE4-FD5D04819844}
Not had a problem with any I've installed.A small red plastic thing that can ping off as soon as you take it out of the box.
Mine did.
I think the only way to keep it on would be to mummify it in self amalgamating tape with some of the tape going round the boom.