Consider TV commercials. Do they make a single case, or do they split their time between 2 different sales pitches? They tend to be quite focused, don't they? Now, the communication tactics in TV ads have been studied and perfected over decades. And the rationale isn't that different for TV compared to websites, since a typical visitor will spend only the briefest period paying attention before clicking "back" or changing the channel.

Presentation influences a visitor's decision-making process. Although you could cram 2 divergent services into a single website, the BEST presentation for a photo gallery and the BEST presentation for training workshops are unlikely to be the same. In fact, they might be mutually exclusive. To optimize both sales pitches and convince the most people, you'll want to separate the landing pages.

Some of your customers for 1 service can be converted into customers for the other service. And you can still take advantage of that audience overlap through on-site ads that link your offerings to one another – not to mention cross-marketing through your transactional emails and newsletter.

The remaining question (from my perspective, anyway) is whether you ought to separate the BRANDS or use a unified brand structure for 2 websites. You might be able to house 2 distinct websites on subdomains within a single domain. Then again, you might want 2 domain names – either related to one another or else pursuing distinct identities.