Promotional clothes are just one of many ways that a business is able to market themselves via the use of promotional products and merchandise. Of course, there isn't anything restricting a company from using both promotional items and promotional clothing, but for argument's sake, what if we say that a business had no choice but to decide between one or the other? Just products or clothing?
When compared to other kinds of promotional merchandise, here is a list of the pros and cons of promotional clothing:
Mobility: Promotional clothes move as the person wearing the garment moves. Therefore, it could be a lot more noticeable than an inanimate object that just resides on a desk or a table, and if the clothes are more eye-grabbing, then the logo and the brand on it should be as well.
They can act as the uniform of your workers: Promotional clothing is often adorned by employees, particularly by tradespeople, in bars and pubs and in stores. This is best when a suit and tie is not appropriate and not suitable for the kind of work involved, but comes across as more professional than the employees wearing their everyday clothes. Not only that, but it's another way of getting the brand seen.
There is more leeway for experimenting: There are so many types of attire available that could be personalised with a logo - hats, hoodies, aprons, sportswear, trousers, coats, fleeces... - that a company does not need to simply stick with the usual promotional polo shirt or t-shirt. Even though promotional products also provide an ultimately endless variety of opportunities, the more unique merchandise could be a lot more costly.
They are not your 'everyday' promotional merchandise: As usual and run-of-the-mill as mugs and pens may be, they are more likely to be handled, used and noticed every day. For a possible client or customer, it is an additional reminder that your products are simply a phonecall away. The same mightn't apply to clothes, particularly depending on the type - e.g. winter wear is season-appropriate, whilst an item of clothing such as an apron might only be appropriate in specific situations.
If given as a gift, they may not be used: In terms of promotional gifts, clothing might not be very appropriate. A pen or mug can be given as a gift and will probably get on-going use. A t-shirt or hoodie though? Maybe not as often, unless we are talking about a musician or band who sells branded clothes. In these instances, promotional products may be more suited.