Working photographers need working lenses - that's either inspired journalism or a tired advertising slogan. Let's see which.
Working photographers work - they make images for someone else, generally in the expectation of being paid. The images they make have to be of such a quality that the customer will let go of the cash willingly. Some customers demand a very high standard indeed in the images - resolution, contrast, depth of field, etc. - but other customers have more modest needs, and the images may reflect this.
If you are shooting for the $ 100,000 customer, shoot the finest glass that your body can sport - and if you are clever get the client to pay for that glass. The Nikon or Canon users can browse in their respective catalogs for wide-aperture primes and zooms and be assured of the best that can be had - they can also look at the Zeiss lenses if they are happy to focus manually. Whatever they get, they will be optically happy, and they can work in very low light levels if need be. These are the workhorses of the photographic stable.
If their client and job is on a more basic level and if there is more natural or artificial light available, then the smaller zooms and primes are a good idea. These can also pay a real benefit in lighter weight and image stabilization - ask a working photographer what it is like carrying a heavy lens versus a light one, but ask at the end of a 12-hour wedding shoot. Be prepared for language.
Here comes the title of this blog - some zooms and primes can be thought of as workponies - small, tough, and able to carry on all day. I know because I use an 18-200 as a standard lens for most field assignments. It let's me have the flexibility to jump instantly from an interior shot of the congregation in a church to the bride and groom at the altar - and instantly is a good thing. Them brides is fast... The school sports photographer or air-show enthusiast would also recognize the advantage. Life sometimes happens without warning.
You've got a good variety of these lenses - Canon and Nikon make excellent 18-200 lenses. Sigma and Tamron do too, and they add a little extra focal length on the long end - out to 250 or 270. Indeed, if you want that extra reach, Nikon do a great 18-300. None of these lenses are bank-breakers - you can pay for them yourself out of the profits...
The size advantage is also something that travelling photographers will appreciate. By all means struggle through the airport with two DSLR bodies, a 24-70 2.8, and a 70-200 2.8... and chargers and batteries and a laptop and a water bottle in a bag and try to stuff them inobtrusively into the overhead locker in the plane. I'll be the one behind you with the 18-200 on my camera in the little bag. At the critical time I will push past you in the airplane aisle. Be prepared for language.