I would say slanging is bad - it can be spammy at times. Abbreviations are also bad - even though they are used to shorten words, it doesn't mean the post isn't spammy.
Here are examples of bad slanging, and bad abbreviation using. 'Hi waaat u doin yo w/o ur tama doing bep it no fun.' OK, so I kind used both in a sentence by being a rapper *_*