If your sales pieces lack unity in their design you'll leave negative impressions. Your business comes across as disorganized and unpredictable.
People want to deal with a company they can count on, that won't throw them surprises. To be trustworthy be consistent.
Likewise, the pieces themselves need unity. Stock photos should be kept to a minimum and preferably not used at all. Every image originating from a different source reduces their cohesiveness.
