This paper is based on the hypothesis that: “Spatial planning should regulate spatial development, taking into account the public and private interests, and enabling the development of public and private investments in construction projects. Investors may be discouraged from construction on account of too small or too excessive a number of spatial implementation conditions (land use guidelines) in particular, where an adequate professional basis has not been provided” This hypothesis has been verified by analyzing spatial planning processes in Poland and Slovenia, two countries whose centrally-planned economies (in Slovenia, this was called the socialist market economy) have been transformed into functioning market economies. The main aim of this study was to discuss the significance of spatial planning documents in the investment process and their contribution to the preservation of spatial order. Special emphasis was placed on planning documents that allow construction in areas not covered by a local zoning plan. In Poland, the relevant document is the outline planning permission for development of land or property. Investors are required to prepare extensive source documents that are used by the (local) authorities for issuing outline permissions for the development of land and of property. Due to a lengthy procedure for obtaining outline planning permission, development is delayed and, as a consequence, investors are discouraged from building. In Slovenia, the relevant spatial plans at the local level include the municipal spatial plan, which set out the spatial implementation conditions and the detailed spatial plan. The spatial implementation conditions are the criteria and conditions for intervention as determined by the spatial planning document, in accordance with which the acquisition of building permits under regulations on construction is prepared. These can have a significant impact on the performance of the investment project. In some cases, such conditions even discourage investors from building, because they are not on an adequate professional basis. The three examples discussed in this paper show that both too general and too precise spatial implementation conditions (land use guidelines) are unfavorable for investors and validate the hypothesis.